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Intrinsically Unstructured Phosphoprotein TSP9 Regulates Light Harvesting in Arabidopsis thaliana
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Department of Biochemistry and Biophysics, Stockholm UniVersity, Stockholm, Sweden.
Department of Plant Biology, UniVersity of Copenhagen, Copenhagen, Denmark.
Department of Biology, Physiology and Molecular Biology, UniVersity of Turku, Turku, Finland.
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2009 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 48, no 2, 499-509 p.Article in journal (Refereed) Published
Abstract [en]

Thylakoid-soluble phosphoprotein of 9 kDa, TSP9, is an intrinsically unstructured plant-specific protein [Song, J., et al. (2006) Biochemistry 45, 15633-15643] with unknown function but established associations with light-harvesting proteins and peripheries of both photosystems [Hansson, M., et al. (2007) J. Biol. Chem. 282, 16214-16222]. To investigate the function of this protein, we used a combination of reverse genetics and biochemical and fluorescence measurement methods in Arabidopsis thaliana. Differential gene expression analysis of plants with a T-DNA insertion in the TSP9 gene using an array of 24000 Arabidopsis genes revealed disappearance of high light-dependent induction of a specific set of mostly signaling and unknown proteins. TSP9-deficient plants had reduced levels of in vivo phosphorylation of light-harvesting complex II polypeptides. Recombinant TSP9 was phosphorylated in light by thylakoid membranes isolated from the wild-type and mutant plants lacking STN8 protein kinase but not by the thylakoids deficient in STN7 kinase, essential for photosynthetic state transitions. TSP9-lacking mutant and RNAi plants with downregulation of TSP9 showed reduced ability to perform state transitions. The nonphotochemical quenching of chlorophyll fluorescence at high light intensities was also less efficient in the mutant compared to wild-type plants. Blue native electrophoresis of thylakoid membrane protein complexes revealed that TSP9 deficiency increased relative stability of photosystem II dimers and supercomplexes. It is concluded that TSP9 regulates plant light harvesting acting as a membrane-binding protein facilitating dissociation of light-harvesting proteins from photosystem II.

Place, publisher, year, edition, pages
2009. Vol. 48, no 2, 499-509 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-16524DOI: 10.1021/bi8016334OAI: diva2:158135
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2010-11-26Bibliographically approved
In thesis
1. Regulatory Functions of Protein Phosphorylation in Plant Photosynthetic Membranes
Open this publication in new window or tab >>Regulatory Functions of Protein Phosphorylation in Plant Photosynthetic Membranes
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxygenic photosynthesis is the process in plants, algae and cyanobacteria which converts light energy from the sun into carbohydrates and at the same time produces oxygen from water. Both carbohydrates and oxygen are essential to sustain life on earth. Sunlight is thus a necessity for life, but it can also cause severe problems for photosynthetic organisms, which have evolved several remarkable acclimation systems to cope with light fluctuations in the environment. In higher plants the light driven reactions of photosynthesis proceed in the chloroplast thylakoid membranes highly organized into stacked regions of grana and interconnecting stroma  lamellae. The grana structure is thought to provide functional benefits in the processes of acclimation of the photosynthetic apparatus, particularly in the quality control of photosystem II (PSII) were photodamaged PSII is repaired in a stepwise manner. These processes in the thylakoid membranes were suggested to be regulated by reversible phosphorylation of several proteins in PSII and in its light harvesting antennae complexes (LHCII). Two thylakoid protein kinases, called STN8 and STN7, have been previously identified as responsible for the phosphorylation of PSII and LHCII, respectively. However, molecular mechanisms and the exact functions of these protein phosphorylation events remained largely unknown.

In this thesis research I have demonstrated that the PSII protein phosphorylation is needed for the maintenance of the thylakoid structure in Arabidopsis thaliana chloroplasts. A big part of the work on characterization of proteins and their phosphorylation has been done using novel mass spectrometry techniques, and we further developed a label-free method for quantitative studies of protein phosphorylation. The phosphorylation of PSII proteins was found to be diurnal regulated and required for maintenance of the cation-dependent functional stacking of the thylakoid membranes. This phosphorylation was further shown to be important for the regulated turnover of the D1 protein of PSII.

Phosphorylation of the plant specific TSP9 protein was found to be dependent on STN7 kinase, and plants deficient in TSP9 showed reduced ability to perform the photosynthetic state transitions and to execute thermal dissipation of excess light energy under high light conditions. I also accomplished characterization of the protein phosphorylation in thylakoids from Arabidopsis plants subjected to high light treatment and discovered STN7-dependent phosphorylation of the antenna protein CP29 required for the adaptive disassembly of PSII supercomplexes in conditions of high light stress.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 42 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1212
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-62303 (URN)978-91-7393-301-8 (ISBN)
Public defence
2010-12-17, Linden, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (English)
Available from: 2010-11-26 Created: 2010-11-26 Last updated: 2010-11-26Bibliographically approved

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